The 12.11Beta is a stand-alone installation, so you won't need to worry about installing the 12.10 suite first. What we do recommend is that after downloading the desired suite (in your case, 12.11Beta), after selecting your language during installation, choose Uninstall->Express. This will remove the existing drivers and will help to ensure that there are no issues with corrupted or conflicting installations on your system. Once the uninstall has finished, reboot and run the file again, choosing Install->Express after selecting your language. The 12.10 CAPs are installed in the 12.11Beta already, the 12.11 is just the 12.10 suite with multiple performance tweaks to see what can be done with the card in terms of game performance, as well as initial attempts to resolve outstanging issues that the Engineers have remedied (like some fluctuating clock speeds in certain CrossFire configurations, which are present in the 12.11Beta7 release.)
So to summarize, you don't have to install 12.10 and the 12.10 CAPs, as these are both in the 12.11Beta, the Beta just features additional tweaks and patches that are not official yet, but do offer better performance for the majority of users.
If you have any other questions or concerns, please do not hesitate to reply to this e-mail directly and I will try to provide any additional information that you may require. Thank you for contacting AMD!